The
majority of small tooth whales are called dolphins. They are mammals
of the order Cetacea and the families Plantanistidae and Delphinidae and
include about 50 species. All have a beak like snout and sharp, conical
teeth. The term porpoise is sometimes applied to many of the same
species, but porpoises, are members of the family Phocaenidae and have
a blunt snout and spade or chisel shaped teeth. The dolphin
fish, is neither a dolphin nor a porpoise. It is a sport fish
related to the mackerels.

Most dolphin species
are about 6 ft in length, the males averaging 4 to 8 in longer than females.
The largest is the killer whale, which can be 19-22ft long and weigh between
8000-10000lbs. One of the largest dolphins is the bottle-nose
dolphin
which can reach over 9ft in length and weigh 440 lbs.
The smallest species is the buffeo, found in the Amazon River. The
buffeo rarely grows over 3.9 ft in length and 66 lbs in weight, really
smalled compared to the bottle_nose.

Dolphins feed on live
food and are predators, except when trained otherwise in captivity.
The primary food is fish, mostly things like herring, mackerel, and sardines.
Some species seem to prefer squid, occasionally, shrimp and other crustacean
are consumed, and even mollusk shells have been found in their stomach
contents. Food consumption is estimated at about 66 lb a day for
an individual about 8.2 ft in length and 220 lb in weight.

The body is sleek and
smooth and the hairless skin is rubbery to the touch. Most species
have jaws that protrude into a beak like snout. Above the upper jaw
is a large mass of fat and oil-containing tissue forming the so-called
"melon" that looks much like a bulging forehead.

The anterior appendages
contain the skeletal remnants of five digits that form the flippers, which
the animal uses primarily as stabilizers, although occasionally in an oar
like fashion. The hind appendages are virtually absent and consist
of a pair of small pelvic bones, deeply embedded in the connective tissue
at the base of the tail. The dorsal fin is formed from subcutaneous
dermal tissue and is not movable by muscle action. The caudal, or
tail, fin is also primarily dermal in origin, rather than skeletal, and
consists of a pair of horizontally extending flukes. The locomotion
of dolphins is typical of the whale. The main thrust comes
from vertical oscillations of the tail and flukes, and most species tested
are capable of sustained swimming speeds of up to 18.6 mph and they jump
at this high speeds travelling 30 ft or more. Their normal "cruising
speed" is about 23 to 25 mph, and if they are bow riding, they have been
known to get up to 30mph. Bow riding is when the dolphin rides teh
bow of a wave produced by a ship.

Because dolphins are
mammals, they must breathe air and maintain a high body temperature.
The internal temperature, between 97.9 deg to 99 deg F, is acheived
by a thick layer of blubber under the skin. Air is breathed through
blowhole, situated almost directly on top of the head. The dolphin
normally comes to the surface to breathe about every two minutes,
and each breath consists of a short, almost explosive exhalation,
followed by a slightly longer inhalation. Dolphins can hold their
breath for up to several minutes and are capable of rapid and deep dives
of more then 1,000 ft.

Dolphins once were
hunted commercially, especially for the small quantity of valuable oil
extracted from parts of the head and used to lubricated delicate watch
mechanisms. Cheaper oils have now been found from other sources,
and dolphins are no longer hunted for this reason. Many dolphins,
however, become accidentally trapped and drowned in tuna nets. Between
the years 1959 and 1972 an estimated 4.8 million dolphins died this way.
Because of the pressure from animal rights activists and United States
consumers, both domestic and international tuna canners have refused to
accept shipments from fishing fleets that do not protect dolphins.
The Marine Mammal Protection Act of 1972, amended in 1988 and 1992, was
passed to prevent exploitation of dolphins and related aquatic animals.
The National Marine Fisheries service is the principal regulatory agency.

Reproduction

Captive dolphins, mostly
the bottle-nose dolphin, has provided us with the reproductive behavior
studies. Mating normally occurs during the spring months, like with
most animals, with the male-female pair exhibiting courtship for some time
prior to the actual mating. A female dolphin has to carry her baby
(calf) for 11-12 months. The calf is delivered normally tail first,
and the newborn is capable of swimming and breathing within the first minutes.
Some mothers have been observed raising the calf to the surface, as if
to help it, but dolphins apparently play in this fashion with a variety
of objects, living or not. This kind of play may have helped the
stories heard round the world of how dolphins have helped humans when they
have been lost at sea, helping them get to the surface and to stay there.

The calf will follow
its mother closely, and suckling takes place frequently, with the mother
tolling slightly and the calf nuzzling the mammary area. The dolphin's
two mammary glands open into a pair of sacs on either side of the anal
opening, and the calf's beak fits into the openings on the sacs.
The nipple is grasped between the upper jaw and the tongue, and muscular
contractions by the mother literally squirt mil into the calf's mouth.
Nursing may continue for as long as 12 to 18 months after birth, although
weaning is probably slowed or inhibited in captive animals.

Communication

Dolphins are extremely
and almost constantly vocal. They are capable of two kinds of sounds.
A specialized mechanism in the nasal passages just below the blow-hole
enables them to emit short, pulse-type sounds. These sounds, called
clicks, can be produced in such rapid succession as to sound like a buzz
or even a duck like quack. The clicks are used as a form of
sonar, in which echoes of sounds from surrounding objects enable the animals
to detect obstacles, other dolphins, fish, and even tiny bits of matter
in the water. The military uses dolphins and this ability to help
them find water minds. This ability is termed ECHOLOCATION.
Some Scientists have speculated that dolphins also use the sounds to deliver
an acoustic shock for stunning of killing small prey.

Deeper in the respiratory
system--presumably in the larynx--dolphins produce another type of sound:
a high pitched whistle of squeal, which is capable of rapid pitch changes.
The whistles differ from the clicks in being essentially single tones.
Apparently the dolphin used the whistles to communicate a particular emotional
state and thus influence the behavior of other dolphins. Typically,
the squeals denote alarm or sexual excitement.

Intelligence

Because dolphins are
highly social and vocalize among themselves with a wide range of sounds,
it has been conjectured that they might possess and almost human like intelligence.
In the 1950s and '60s the American neurologist John Lilly conducted well publicized experiments based on this concept,
in which he attempted to communicate with dolphins in their own "language,"
but other scientists have rejected his work as poorly documented and lacking
scientific validity.

Because of the ability
of dolphins to learn and perform complex tasks in captivity, their continuous
communications with one another, and their ability, through training, to
approximate the sounds of a few human words, some investigators have suggested
that the animals might be capable of learning a true language and communicating
with humans.

Dolphins can be found
in virtually all the seas and oceans of the world. Some species are
sharply restricted, but many, like the common
dolphin, Delphinus delphis, or the bottle
nose dolphin, are found worldwide. Several species are found
in fresh water, notably the Ganges River dolphin, Platanista gangetica;
the rivers of South America are the home of the long-snouted dolphin, Inia
geoffrensis, and the small, graceful Sotalia fluviatilis, occasionally
seen as far as 1,553 miles up the Amazon River.

Dolphins are quite
abundant in some areas of the world. Off the coast of Japan, for
example, populations of the white-sided
dolphin, are estimated at 30,000 to 50,000 individuals. In many
species, schools of up to 1,000 travel together, while some species, such
as the bottle-nose dolphin, tend to be found in smaller groups of less
than 100.

Dolphins
and Humans

Dolphins adapt well
to human companionship and are readily trained. Bottle-nose dolphins
have become well known performers in may aquariums; they are capable of
spectacular tricks and may mimic the sounds of a few human words.